Nepal quake reminder of Washington’s tectonic influences

The U.S. Geological Survey produced a report on the magnitude 7.8 earthquake that struck Nepal April 25 and the surrounding aftershocks that continued throughout much of south central Asia.

The magnitude 7.8 earthquake that devastated the Kathmandu Valley of Nepal Saturday was the strongest quake in the world so far this year and a reminder of the importance of properly planning in advance for natural disasters. More than 4,000 were reported dead, as buildings collapsed in cities surrounding the fault line.

The shallow depth of the quake’s epicenter was placed between 7 and 10 miles. Waves were amplified through sedimentary basin of a former lake, increasing the destruction. The strength of the quake was so strong it was picked up by a Pacific Northwest Seismic Network seismometer at Gold Mountain on the Kitsap Peninsula.

Saturday’s earthquake was the result of the northward movement of the Indian tectonic Plate under the Eurasian Plate. The plate lurched some 10 feet over 30 seconds, the LA Times reported.

The Indian Plate met the Eurasian Plate some 40 to 50 million years ago. The Indian Plate is forced beneath the Eurasian Plate as it continues its northward move. The joining of the two faults is called a “suture” and is revealed by the increasing elevation of the Himalaya Mountains.

This Wall Street Journal image of the collision between the Indian Plate and the Eurasian Plate at Tibet shows the similarities the subduction zone has to the Cascadia subduction zone off Washington’s coast.

The two plates interact not entirely differently than the Juan de Fuca Plate and the North American Plate, an area known as the Cascadia subduction zone, the 750-mile fault line that runs off the coast of Washington, Oregon, Northern California and British Columbia.

The very significant difference is that the Cascadia Plate is an oceanic plate, so our subduction zone doesn’t produce the same high peaks as the two continental plates, according to Chief Hazards Geologist Tim Walsh.

DNR geologists have produced models of what impacts an earthquake from the Cascadia subduction zone could do at differing magnitudes. We’re also developing models of tsunami inundation in population centers both along the Washington coast and within the Puget Sound to help communities plan for the impacts that would likely occur from a tsunami stemmed by a Cascadia quake.